Many cheap, “made in China”, MP3 players also have video playing capabilities. In spite of the low display quality these devices can be used to view in a satisfying way many low quality videos like for example Youtube videos.
Unfortunately the video format used, identified by the AMV or by the MTV extension, is out of common video format standards because specifically studied to be suitable to very low-end hardware. In addition conversion software provided with the players is Windows-only (and often a little buggy).
I recently discovered how to use Linux to convert videos to AMV video format. (It’s a recent discover only to me since the project is dated 2007)